Locking means for turbine or compressor blading



Oct. 9, 1962 J. A. BOYLE ET AL 3,957,598

LOCKING MEANS FOR TURBINE OR COMPRESSOR BLADING Filed July 1, 1960 w 3 MARTHUR 60YLE 50am Game? GAR/4614 Arte/a NEYS United States Patent Ofiice3,057,598 Patented Oct. 9 1962 3,057,598 LOCKING MEANS FOR TURBINE RCOMPRESSOR BLADING John Arthur Boyle, Sale, and John George Garnett,Winton, Eccles, England, assignors to Associated Electrical IndustriesLimited, London, England, a British com- Filed July 1, 1960, Ser. No.40,315 6 Claims. (Cl. 253--77) This invention relates to means forlocking in position the blades of turbine type machines or compressorsto prevent their movement in an axial direction, of the kind in whichthe blades have an axial root fixing in slots or grooves around theperiphery of the rotor or equivalent retaining body, the slot beingformed with an overhanging shoulder or shoulders preventing removal ofthe blade from its slot in a radially outward direction. Such a bladeattachment assembly is herein referred to as of the shoulder type and isexemplified by the well-known fir-tree assembly.

Various methods of locking have been proposed, for example caulking,also various arrangements of locking plates located between the bladeroot and the slot and them up at the ends so as to engage the sides ofthe blade root and slot. British patent specification No. 691,380describes a simple arrangement effective for small machines whichcomprises a locking device made up of strip metal which is disposed atthe bottom of the slot and is longer than the length of the slot, theextending ends of the strip having lateral extensions, which are bentabout a transverse line of the strip to closely engage adjacent endfaces of the blade root and the body portion on a side of the slot. Suchlocking plates have however not been found satisfactory in the designsand manufacture of locking means for large heavy blades. The crosssectional area in such cases has to be designed for robustness withconsequent loss of flexibility necessary to permit of full close contactagainst the faces of the retaining body; this area of strip materialrequired to hold the blades from movement in an axial direction createsdifficulty in closing as a final operation of assembly.

According to the present invention a locking means for a bladeattachment assembly of the shoulder type including an axially extendinggroove at the bottom of the slot beneath the blade root comprises aU-shaped retaining plate and a locking plate located side by side in thebottom of the slot and filling the space between the walls of the grooveand the tip of the blade root, the retaining plate being formed of afiat bar of the same length as the blade root and slot with anupstanding leg at each end arranged to contact the sides of the bladeroot and the retaining body, one leg of the U having a profile suchthat, when fitted over the tip of the blade root, the U-shaped plate iscapable of axial insertion into the slot, Without fouling the retainingshape of the slot wall, the width of the bar being such as to leave agap along the side of the groove when placed therein, and the lockingplate extending along the gap between the bar and one side of the grooveto hold the bar against the opposite side of the groove with the legsoverlying the blade root and retaining body, the ends of the lockingplate being formed (e.g. bent over) so as to engage the sides of theretaining body and prevent axial movement therein.

With the use of the locking means according to this invention, thecomponent which prevents axial movement of the blade is no longer lockedin position in the retaining body by deformation of a stressed portion.It can therefore be produced by direct mechanical means as a preformedunit and be designed for robustness since the requirement for sufiicientfiimsiness to bend close against the body by hand is now removed. Thelocking'plate still has to be closed by hand but, as the constructionhas re. moved all axial stress from this plate, its cross-sectional areacan be appropriately designed or the necessity for full closing contacton to the retaining wheel or body be removed.

The invention may be better appreciated from a consideration of thefollowing description of the accompanying drawings which refersspecifically to blades and slots having a fir-tree serrated shape, butthe invention is applicable to any shape where the blade is preventedfrom moving outwards radially by the action of any undercut surfaceproviding an overhanging shoulder.

In the drawings FIG. 1 is a perspective view of a preformed U-shapedretaining plate, FIG. 2 is a similar View of a preformed locking plate,FIGS. 3-5 illustrate successive stages in the assembly of a blade in aslot with the locking means of FIGS. 1 and 2 and FIG. 6 is a view on theline 66 of FIG. 5. FIG. 7 is a modified form of FIG. 2.

As shown in FIG. 1, the retaining plate 1 comprises a rectangular bar 2with upstanding legs 3 at each end forming a member of generallyU-shape. FIG. 2 shows a locking plate 10 made of strip material whichmay be preformed by bending one end 11 out of the plane of the strip.

The retaining body is depicted in axial end view in FIGS. 3-5 as part ofa turbine or compressor rotor 5 with a slot 6 for receiving a blade root7 of fir-tree shape.

The inner end or bottom of the slot terminates in a groove 8 in whichthe bar 2 of plate 1 is located.

The retaining plate 1 is designed so that the inner faces of the legs 3are spaced apart by a distance which will allow them to fit over theends of the blade root 7, as best seen in FIG. 6. The width of the legswhen viewed lengthwise of the bar 2 is sufficient to allow one side tooverlie the body 5 when the bar is against one side of groove 8, as seenin FIGS. 4 and 5. The width of the bar 2 is such as to permit ofcircumferential movement of the bar to one side of the groove andprovide a gap 9 at the other side, as shown in FIG. 4. The overhangingside 10f one at least of the legs 3 (the right hand side in FIGS. 3-5 isgiven a profile 4 such that the plate 1 may be slid axially along theslot 6 clear of the serrated retaining shape thereof. FIG. 1 shows bothlegs cut away at 4,

thus enabling either end of the plate to be inserted into the slot.

With the foregoing construction the retaining plate may be madesufiiciently robust and of material strong enough to withstand the axialstresses set up due to any'tendencyf of the blade root to move in theslot, whilst the locking plate can be of lighter construction, since noaxial force'- is applied to it, enabling it to be readily bent over byhand against the side of the rotor body 5.

into the slot 6 in the retaining body (FIG. 3) and the U-shaped plate isthen moved in a circumferential direction to the rotor so that the baseof the plate contacts one side of groove 8 and the shaped legs of theplate overhang the sides of the body 5 as shown in FIG. 4. Thus as theblade root is contained within the legs of the U-shaped plate and as theplate overhangs the sides of the rotor body, the blade is prevented fromhaving axial movement.

The locking plate 10 is next inserted axially into the gap 9 between theother side of the groove 8 (i.e. the left side in FIGS. 4 and 5) and theside of the part 2 of the plate 1. The plate 10 is then locked inposition by forcing 3 the end that is not preformed against the side ofthe body 5 as seen at the right hand side of FIG. 6. Obviously if thelocking plate is a fiat unbent strip, both ends will be bent over. Itwill be seen from FIG. 5 that the plate prevents the bar 2 from movingin the groove so that the axial movement of the assembly is prevented.

Since no axial force is applied to it the plate 10 is only required tobe of nominal thickness, though it Will usually be of the same thicknessas the U-shaped plate 1, so as to leave as little clearance as possiblebetween it and the tip of the blade root.

One advantage of the method of locking described above is that theblades can be inserted along the length of the groove in eitherdirection and this is necessary in certain cases of blade profileshaving a large angle of twist from root to tip.

Another advantage is that it facilitates the assembly of blades in asolid gashed rotor having a number of retaining discs or wheels on onespindle, each of which has grooves for the retaining of blades; anotheradditional advantage is that the main U-shaped retaining plate is notexpendable on reblading, as only the cheaper locking plate will have tobe renewed when the blades are replaced.

It will be appreciated that modifications of the con structionillustrated may be made without departing from the scope of theinvention described herein. For example the preformed locking plate mayconsist of two or more legs connected at one end by a yoke, the platebeing shaped to suit the radius of the bottom of the slots with the legsspaced apart a distance equal to the pitch of the slots so as to fitbeneath the blade roots. With this form the yoke may lie in the plane ofthe legs or it may be bent as in the case of a single strip. A suitabletype of preformed plate with two legs 10 connected by a yoke 12 bent atan angle to the legs is illustrated in FIG. 7. In some cases it may besufiicient for one leg only of the plate 1 to be profiled, the otherbeing for example rectangular. However profiling both legs enables theplate to be inserted into the slot from either side of the body. In afurther modification both sides of the leg(s) may be profiled,permitting circumferential movement in the slot in either directionduring assembly.

Although in the foregoing the invention has been described withparticular reference to axially directed slots, it is understood that itmay equally Well be applied to assemblies with a skew-axial fixing.

What we claim is:

1. In combination, a rotor body having an axially extending slot in itsperiphery, a blade having a root fitting in said slot and radiallyretained therein by an attachment of the shoulder type, the slot androot having co-operating portions spaced apart radially thereby formingan axially extending groove at the bottom of the slot beneath the bladeroot, and means for retaining the root in axial position in the slotincluding a preformed U-shaped retaining plate and a locking plateextending side by side through said groove, said retaining plate beingformed of a flat bar of the same length as the blade root and slot withan upstanding leg at each end arranged to contact the sides of the bladeroot and the rotor body, one leg of the U having a transverse dimensionsmaller than that of said slot and a profile such that, when saidU-shaped plate is fitted over the tip of the blade root, said root andplate together are capable ofaxial insertion into the slot without saidplate fouling the retaining profile of the slot wall, the bar beingnarrower than the groove so as to leave a gap extending along the sideof the groove when placed therein, and the locking plate extending alongthe gap at one side of the groove to hold the bar against the oppositeside of the groove with the legs overlying a part of the blade root andof the rotor body, the ends of the locking plate in the assembly beingangularly disposed to engage the sides of the rotor body and preventaxial movement therein.

2. The combination claimed in claim 1, in which both said retainingplate legs are profiled on the same side to conform substantially withthe retaining profile of said slot wall.

3. The combination claimed in claim 2, in which said legs areadditionally profiled in like manner on their other sides therebyproviding a plate of symmetrical form.

4. The combination claimed in claim 1, in which said locking plateconsists of a plurality of legs connected at one end by a yoke, theplate being shaped to suit the radius of the bottom of the slots withthe legs spaced apart a distance equal to the pitch of the slots so asto fit beneath the blade roots.

5. The combination claimed in claim 4, in which the said yoke is bentsubstantially at right angles to the legs so as to lie against the sideof the rotor body.

6. In combination, a rotor having an axial surface slot of uniformwidth, a blade having a root of the same axial length as said slotaxially inserted into said slot, cooperating interlocking formations onsaid root and in said slot radially retaining the blade on the rotor,said slot being of such depth as to provide an axial groove beneath theroot, a preformed U-shaped retainer plate having a bar narrower than thegroove axially extending along said groove and end legs bridging theopposite sides of the rotor and blade root, at least one of said legsbeing profiled to enable axial insertion of the blade root and retainerplate together in assembly into said rotor slot, and said retainer platebar being shiftable circumferentially of the rotor in said groove afterthe blade root and retainer plate together have been axially insertedinto the slot to locate said legs to bridge the root and rotor sides,and a locking plate extending axially along said groove beside said bar,said locking plate having at least one straight end prior to assemblyfor insertion endwise into said groove after the blade root and retainerplate have been installed on the rotor to occupy remaining groove widthand retain said bar against displacement eircumferentially of the rotor,and both locking plate ends extending in the assembly to engage therotor sides and prevent axial displacement of the locking plate.

References Cited in the file of this patent UNITED STATES PATENTS2,801,074 Brown July 30, 1957 FOREIGN PATENTS 691,380 Great Britain May13, 1953

